U.S. patent number 5,202,185 [Application Number 07/695,372] was granted by the patent office on 1993-04-13 for sheath-core spinning of multilobal conductive core filaments.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Harry V. Samuelson.
United States Patent |
5,202,185 |
Samuelson |
April 13, 1993 |
Sheath-core spinning of multilobal conductive core filaments
Abstract
Multilobal core conductive bicomponent sheath-core filaments are
provided and methods for making the same.
Inventors: |
Samuelson; Harry V. (Chadds
Ford, PA) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
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Family
ID: |
26999103 |
Appl.
No.: |
07/695,372 |
Filed: |
May 3, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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356051 |
May 22, 1989 |
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Current U.S.
Class: |
428/373; 428/368;
428/372; 428/374; 428/397; 57/248 |
Current CPC
Class: |
D01D
5/253 (20130101); D01D 5/34 (20130101); D01F
1/09 (20130101); Y10T 428/2927 (20150115); Y10T
428/2931 (20150115); Y10T 428/2929 (20150115); Y10T
428/292 (20150115); Y10T 428/2973 (20150115) |
Current International
Class: |
D01F
1/09 (20060101); D01D 5/253 (20060101); D01D
5/34 (20060101); D01D 5/00 (20060101); D01F
1/02 (20060101); B32B 009/00 () |
Field of
Search: |
;428/372,373,374,368,397
;57/248 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ryan; Patrick J.
Assistant Examiner: Edwards; N.
Parent Case Text
RELATED APPLICATION
This application is a continuation-in-part of my application Ser.
No. 07/356,051 filed May 22, 1989, now abandoned.
Claims
I claim:
1. A novel synthetic sheath-core bicomponent filament having
antistatic properties comprising a continuous nonconductive sheath
of a synthetic thermoplastic fiber forming polymer selected from
the group consisting of polyester and polyamide surrounding an
electrically conductive polymeric core, constituting from 0.3% to
35% of the filament cross-section, said polymeric core comprised of
20 to 35% of electrically conductive carbon black dispersed in
polyethylene, the cross-section of said core having from three to
six lobes and a modification ratio of at least 2, with each lobe
having an L/D ratio of from 1 to 20, where L is the length of a
line drawn from the center point of the line between low points of
adjacent valleys on either side of the lobe to the farthest point
on said lobe, and D is the greatest width of the lobe as measured
perpendicular to L.
Description
BACKGROUND OF THE INVENTION
Synthetic filaments having antistatic properties comprising a
continuous nonconducting sheath of synthetic polymer surrounding a
conductive polymeric core containing carbon black have been taught
by Hull in U.S. Pat. No. 3,803,453. The cross-section of the core
shown in said patent is circular. Need has arisen in certain
end-use applications, such as career apparel worn in clean rooms,
for even greater reduction of static propensity, and contrary to
the desires expressed by others to conceal the fiber blackness, is
a desire for greater visibility of the core.
Sheath-core filaments wherein the cross-section of the core is
trilobal are known. They can be prepared with a spinneret of the
type shown in U.S. Pat. No. 2,936,482. While useful products of the
invention can be prepared with such spinnerets, improvements in
preserving definition of the trilobal core through the spinning
process is a worthwhile objective. The present invention offers an
improved spinning technique as well as providing a novel filament
which rapidly dissipates electrical charges.
DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are schematic cross-sectional views of sheath-core
filament of the invention illustrating trilobal and tetralobal
cores as well as showing how the required structural parameters are
determined.
FIG. 3 is a fragmentary section of a distribution and spinneret
plate taken along line 3,3 of FIG. 4.
FIG. 4 is a bottom view of the distribution plate of FIG. 3.
SUMMARY OF THE INVENTION
The present invention has two important aspects. It provides a
novel synthetic filament having antistatic properties comprising a
continuous nonconductive sheath of a synthetic thermoplastic
fiber-forming polymer surrounding an electrically conductive
polymeric core comprised of electrically conductive carbon black
dispersed in a thermoplastic synthetic polymer, the cross-section
of said core having from three to six lobes and a modification
ratio of at least 2, with each lobe having an L/D ratio of from 1
to 20, where L is the length of a line drawn from the center point
of the line between low points of adjacent valleys on either side
of the lobe to the farthest point on said lobe, and D is the
greatest width of the lobe as measured perpendicular to L. It also
provides an improved process for better maintaining the core
definition during melt-spinning of a sheath-core fiber wherein one
polymer composition constitutes the sheath component and a
different polymer composition constitutes the core component and in
which the core has three or more lobes. The process comprises
simultaneously extruding the molten sheath and core component
compositions through a spinning orifice with the sheath component
completely surrounding the core component, the improvement
comprising, maintaining the core cross-sectional configuration
by
1) feeding the molten core component composition in the desired
multilobal cross-section through a channel opening above a
spinneret capillary,
2) feeding the molten sheath component from all directions against
the core along the periphery of the entrance to the spinneret
capillary to completely surround the core component,
3) controlling the flow of molten sheath component composition at
spaced sections along the periphery of the spinneret capillary
entrance to allow more to flow to zones between the lobes than to
zones at the lobes, and
4) solidifying the molten components after leaving the spinneret
orifice.
DETAILED DESCRIPTION OF THE INVENTION
Static dissipating fibers are well-known in the art and have been
used for many years in textiles. A particularly successful fiber
has been the fiber described in U.S. Pat. No. 3,803,453. This fiber
is a sheath-core bicomponent fiber prepared by melt co-extrusion of
two thermoplastic compositions as sheath and core, respectively.
The sheath is nonconductive. The core polymer is made conductive by
incorporation of electrically conductive carbon black. The sheath
provides strength to the fiber, hides the black core, and protects
the core against chipping and flaking which can occur if the core
were exposed at the fiber surface. Certain present day end-use
applications require greater anti-static effect with less concern
for color. In distinction, there is a greater desire to see more
core color as a means of distinguishing in use those garments which
are protected from those which are not. Applicants have found that
this can be accomplished by modifying the sheath-core fiber of U.S.
Pat. No. 3,803,453. The modification consists primarly of employing
a core, of the same composition as in said patent but having a
cross-section with from three to six lobes, a modification ratio of
at least 2, and with each lobe having an L/D ratio of from 1 to 20.
FIG. 1 shows such a cross-section.
FIG. 1 is a schematic cross-sectional representation of a
sheath-core fiber wherein a trilobal core is surrounded by a sheath
as might be seen on an enlargement of a photomicrograph. The nature
of the core and sheath will be discussed in greater detail below.
The determination of modification ratio is known in the art but,
for convenience, it can be defined by reference to FIG. 1. The
modification ratio is the ratio of the radius of the smallest
circle circumscribing the trilobal core to the radius of the
largest circle which can be inscribed in the trilobal core where
the lobes meet. In FIG. 1, this is A/B.
Determination of the L/D ratio for the lobes is also illustrated by
reference to FIG. 1. A first line is drawn connecting the low
points of adjacent valleys on either side of a lobe and another
line L is drawn from the center of the first line to the farthest
point of said lobe. The value D represents the greatest width of
the lobe as measured perpendicular to L. FIG. 2 is a schematic
showing a cross-section of a round fiber having a tetralobal
core.
Spinning of the filaments of the invention can be accomplished by
conventional two-polymer sheath-core spinning equipment with
appropriate consideration for the differing properties of the two
components. The filaments are readily prepared by known spinning
techniques and with polymers as taught, for example, in U.S. Pat.
No. 2,936,482. Additional teaching of such spinning with polyamides
is found in U.S. Pat. No. 2,989,798. A new improved process has
been developed to better preserve the definition of sheath-core
bicomponent fibers having tri-, tetra-, penta- or hexalobal cores
as they are extruded. This is described below.
The improved process employed for spinning the sheath-core
bicomponent yarn of Examples 1 and 2 below, is a modification of a
conventional sheath-core bi-component melt-spinning process. In the
conventional process, the core feed polymer stream and the sheath
feed polymer stream are fed to a spinneret pack including filters
and screens, and to a plate which distributes the molten polymer
streams to orifices that shape the core and surround it with
sheath. Reference to FIGS. 3 and 4 will assist in the understanding
of the modified process. Core polymer is fed to channel 2 and exits
over the entrance to capillary 3 of spinneret plate 5. Sheath
polymer is fed through passageway 7 of plate 8 into the space
between plates 5 and 8, maintained by shims not shown. This polymer
is fed from all directions against the core polymer stream in the
vicinity of the entrance to the spinneret capillary 3 and both
streams pass through capillary 3 in sheath-core relation, finally
exiting from the spinneret orifice, not shown, at the exit of
capillary 3. The improved process maintains better definition of
the core lobes. This is accomplished by controlling the flow of
molten sheath component composition against the core polymer stream
at spaced sections along the periphery of the entrance to the
capillary to allow more sheath polymer to flow to zones between the
lobes than to zones at the lobes. This can be achieved by enlarging
the passageway for the sheath polymer to the capillary only in
those sections leading to zones between lobes. Thus, as shown in
FIGS. 3 and 4, depressions 10 were etched in plate 8 to permit
increased sheath polymer flow to regions between lobes.
The filament sheath may consist of any extrudable, synthetic,
thermoplastic, fiber-forming polymer or copolymer. This includes
polyolefins, such as polyethylene and polypropylene, polyacrylics,
polyamides and polyesters of fiber-forming molecular weight.
Particularly suitable sheath polymers are polyhexamethylene
adipamide, polycaprolactam, and polyethylene terephthalate.
Tensile and other physical properties of the filaments of the
invention are primarily dependent on the sheath polymer. For high
strength filaments, polymers of higher molecular weight and those
permitting higher draw ratios are used in the sheath. While undrawn
filaments of the invention may provide adequate strength for some
purposes, the drawn filaments are preferred. In some applications,
for example where the filaments of the invention are to be
subjected to high temperature processing with other filaments such
as in hot fluid jet bulking or other texturing operations, it is
important that the sheath polymer have a sufficiently high melting
point to avoid undue softening or melting under such
conditions.
The filament core of the antistatic fibers consists of an
electrically conductive carbon black dispersed in a polymeric,
thermoplastic matrix material. The core material is selected with
primary consideration for conductivity and processability as
described in detail in U.S. Pat. No. 3,803,453. Carbon black
concentra-tions in the core of 15 to 50 percent may be employed. It
is found that 20 to 35 percent provides the preferred level of high
conductivity while retaining a reasonable level of
processability.
The core polymer may also be selected from the same group as that
for the sheath, or it may be non-fiber forming, since it is
protected by the sheath. In the case of non-antistatic fibers, the
core of the bicomponent fiber will, of course, be
non-conductive.
The cross-sectional area of the core in the composite filament need
only be sufficient to impart the desired antistatic properties
thereto and may be as low as 0.3 percent, preferably at least 0.5
percent and up to 35 percent, by volume. The lower limit is
governed primarily by the capability of manufacturing sheath/core
filaments of sufficiently uniform quality while maintaining
adequate core continuity at the low core volume levels.
Conventional drawing processes for the filaments can be used but
care should be exercised to avoid sharp corners which tend to break
or damage the core of the antistatic fibers. In general, hot
drawing, i.e., where some auxiliary filament heating is employed
during drawing, is preferred. This tends to soften the core
material further and aid in drawing of the filaments. These
antistatic filaments may be plied with conventional synthetic,
undrawn filaments and codrawn.
For general applications, the filaments of this invention have a
denier per filament (dpf) of less than 50 and preferably less than
25 dpf.
The filaments of this invention are capable of providing excellent
static protection in all types of textile end uses, including
knitted, tufted, woven and nonwoven textiles. They may contain
conventional additives and stabilizers such as dyes and
antioxidants. They may be subjected to all types of textile
processing including crimping, texturing, scouring, bleaching, etc.
They may be combined with staple or filament yarns and used as
staple fibers or as continuous filaments.
Said filaments may be combined with other filaments or fibers
during any appropriate step in yarn production (e.g., spinning,
drawing, texturing, plying, rewinding, yarn spinning), or during
fabric manufacture. Care should be taken to minimize undesirable
breaking of the antistatic filaments in these operations.
Upon exiting the spinneret orifice, the bicomponent stream cools
and begins to solidify. It is generally not desirable to apply too
high a spin stretch with the conductive fibers since quality as an
antistatic fiber diminishes. This is not a limitation with other
bicomponent fibers.
TEST PROCEDURES
Tenacity and elongation of yarns were measured using ASTM
D-2256-80. The method for determining relative viscosity (LRV) of
polyester polymers is described in U.S. Pat. No. 4,444,710 (Most).
The method for determining relative viscosity (RV) of polyamides is
disclosed in U.S. Pat. No. 4,145,473 (Samuelson). Surface
resistivity of fabrics is determined using AATCC Test Method
76-1987. Electrostatic propensity of carpets is measured using
AATCC Test Method 134-1986. Static decay data are measured using
Method 4046 (Mar. 13, 1980), Federal Test Method Std. No. 101C. The
modification ratios and L/D ratios were measured from
cross-sections on photomicrographs as well understood in the
art.
The following examples, except for controls, are intended to
illustrate the invention and are not to be construed as limiting.
Multilobal core filaments of the invention are described in each of
Examples 1 to 3.
EXAMPLE 1
Sheath-core filaments having a sheath of 23.5 LRV polyethylene
terephthalate and a polyethylene core that contained 28.4% carbon
black were spun and wound up without drawing at 1200 meters per
minute. The conductive core constituted 6% by weight of these
filaments, and the yarns, which contained six filaments, were
subsequently heated to 140.degree. C. and drawn at the ratios
listed in Table I. Samples with a round conductive core were spun
using a spinneret assembly similar to that shown in FIG. 11 of U.S.
Pat. No. 2,936,482, whereas those having trilobal shaped cores were
spun by the improved process of this invention using the spinneret
assembly and plate shown in FIGS. 3 and 4. The modification ratio
of the trilobal conductive core was 5 and the L/D ratio was 3. The
trilobal core yarns were darker than the round core yarns. After
drawing, these yarns were incorporated into a 100% polyester 28 cut
jersey knit by feeding in the conductive core yarns at 5/16 inch
intervals. Yarn and fabric properties measured on these samples are
shown in Table I:
TABLE I ______________________________________ Core Shape Round
Trilobal Draw Ratio 2.35.times. 2.10.times. Total Denier 35.9 40.0
Tenacity, g/d 1.81 1.61 % Elongation 28.9 21.4 Fabric Properties
Surface Resistivity 1.5 .times. 10.sup.13 1.9 .times. 10.sup.12
ohms/unit sq. Federal Test Method 4046 Standard 101C (90% Decay)
Time in sec./2 sec. charge level From: +5 KV 33/900 0.23/275 -5 KV
9.5/-950 0.20/-300 ______________________________________
The fabric containing the yarn with the trilobal shaped conductive
core had significantly lower surface resistivity and much faster
static decay times than that made with the yarns having round
conductive cores.
EXAMPLE 2
Sheath-core filamentary yarns (40 denier 6 filaments) having a
sheath of 46 RV 66-nylon and either round or trilobal shaped
conductive cores similar to those described in EXAMPLE 1 were
prepared, except they were drawn at 110.degree. C. using a
3.2.times. draw ratio. The modification ratio of the trilobal
conductive core was 4 and the L/D ratio was 2. These conductive
core fibers were plied with 1225 denier nylon carpet yarn and
direct tufted into level loop carpets. Both carpets were evaluated
in the AATCC Test Method 134. The carpet containing the yarns with
trilobal shaped cores had a significantly lower measurement of 0.8
KV versus 1.2 KV for the carpet made from yarns having round
conductive cores.
EXAMPLE 3
Utilizing spinneret assemblies as described in FIG. 11 of U.S. Pat.
No. 2,936,482, sheath-core products were produced having a 24%
central conductive core surrounded by a 76% sheath of polyethylene
terephthalate. Filaments having either round or trilobal
(modification ratio of 2.0, L/D of 1.0) shaped conductive cores
were prepared, and the cores contained 32.0% carbon black ("Vulcan
P", available from Cabot Corp.), compounded into a film grade
equivalent high melt index, low density polyethylene.
The resulting fibers were air quenched at 21.degree. C., drawn
1.84.times. and wound up at 1372 meters per minute as a 35 denier 6
filament product. After heat annealing (130.degree. C.) to reduce
shrinkage, the products were woven into fabric for static
dissipation evaluation.
Woven fabrics were prepared as follows:
Non-Conductive Yarns--150 denier, 34 filaments--3.3 Z twist
polyester fiber
Static Dissipative Yarns--100 denier, 34 filaments--4 S twist
polyester fiber plus one static dissipative yarn as described
above.
Weaving:
96 ends, 88 picks, 8.times.8 herringbone
Warp--1 Static dissipative yarn and 23 non-conductive ends.
Filling--2 Static dissipative yarns and 22 non-conductive
picks.
Fabrics:
A. Contains Trilobal Core
B. Contains Round Core
Electrostatic Properties
Yarn Resistivity, ohms/cm (length)--as prepared.
A. 3.7.times.10.sup.11
B. 7.4.times.10.sup.11
Fabric Resistivity (AATCC 76-1987) ohms/unit square after
heat-setting and scouring
A. warp-2.9.times.10.sup.12, fill-2.7.times.10.sup.12
B. warp->1.times.10.sup.14, fill->1.times.10.sup.13
EXAMPLE 4
Sheath-core filaments were prepared with polyethylene terephthalate
sheath and trilobal shaped conductive cores made from carbon black
dispersed in polyethylene as described in Example 1, and which
constituted 12% by weight of the filaments. These yarns were spun
at 600 meters/minute, and then in a separate step they were drawn
to a 3.times. draw ratio over a 110.degree. C. hot plate, and wound
up at 300 meters/minute so that the final yarn denier-yarn count
was 40-6. Sample C was spun with the spinneret pack described in
Example 1, while sample D was spun with the same spin pack except
that the small cutouts in the plateau which increased polymer flow
into the trilobal saddle were absent. The trilobal shaped core in
sample C had a modification ratio of 3.0 and a L/D of 1.4, whereas
the core in sample D had a 1.5 modification ratio and a L/D of 0.6.
Plain woven fabrics were prepared as follows:
Non-conductive yarns--70 denier, 34 filament polyester
Weaving--110 ends/inch (warp), 76 picks/inch (fill), with 2 of the
static dissipative yarns inserted in the fill direction after every
34 non-conductive picks.
The woven fabrics were after-scoured and rinsed to remove all
residual finish, and then tested using a corona discharge test in
which cut samples from the fabrics were placed on a grounded metal
plate and charged to 10,000 volts using a 10,000 volt corona. Then
the residual electric field intensities were measured two seconds
after charging to determine the residual charge. When the woven
fabric containing sample C (having trilobal core with 3.0
modification ratio) was tested, the residual charge was 750
volts/inch, while the woven fabric containing sample D (1.5
modification ratio core) had 2450 volts/inch residual charge, and a
plain woven control fabric that lacked any static dissipative yarns
had 7000 volts/inch residual charge.
Although the apparatus shown in FIGS. 3 and 4 was used to prepare
sample C and the trilobal shaped core samples in Examples 1 and 2,
other means can be employed. A thin shim (0.001-0.010 inches) can
be placed between the distribution plate and spinneret to control
polymer flow axially to the triobal capillary legs and allow the
sheath polymer to flow into the zones between the lobes to maintain
the desired shape and thickness.
* * * * *